LISTBOX SELECTED ITEM CHANGED FROM JAVASCIPT DOES NOT FIRE SERVER SIDE EVENT

I have a listbox with searchable entries. Search is achieved using textbox.

<script type="text/javascript">
        function fnSearchListBox() {
            var strSearchValue = document.getElementById('<%= txtsSearchSernm.ClientID %>');
            if ($("#txtsSearchSernm").val().length == 0) {
                fnClearSelection();
            }
            for (var i = 0; i < document.getElementById("lstSServices").options.length; i++) {
                if (document.getElementById("lstSServices").options[i].text.toLowerCase().match(strSearchValue.value.toLowerCase())) {
                    document.getElementById("lstSServices").options[i].selected = true;
                   //document.getElementById('lstSServices').options[i].style.color = "blue";

                    return false;
                }
                else {
                    fnClearSelection();
                }
            }
        }


        function fnClearSelection() {
            document.getElementById("lstSServices").selectedIndex = -1;

            
        }
    </script>

<asp:ListBox ID="lstSServices" runat="server" Height="203px" Width="272px"
                                            SelectionMode="Single"
                                            onselectedindexchanged="lstSServices_SelectedIndexChanged" AutoPostBack="true"></asp:ListBox><asp:TextBox ID="txtsSearchSernm" runat="server" CssClass="textfield-mandatory" Width="264px"
                                            placeholder="Service Name" onkeyup="fnSearchListBox();" AutoComplete="off"></asp:TextBox>

If i click on any item in lisbox then list box click event

lstSServices_SelectedIndexChanged 

get fired. But after searching something, the matched value is highlighted using javascript, on click of that matched value the  selectedindex changed event does not fire .

help pls